408 ON THE COLUMELLA OF ICHTHYOSAURUS. [June 29, 
displaying an uncrushed inner view: the bone, however, though well 
shown in Mr. O’Neill’s drawing, is not specially marked, and it is 
therefore advisable to append a separate sketch, such as is given in 
the woodcut, fig. 3 (p. 407). The general outline is similar to that 
of the examples already described, but the additional characters of 
the inner aspect are well worthy of note. In the constricted portion 
of the bone, the shaft is compressed to form a sharp ridge, which 
terminates in an abrupt prominence at the point where the lower 
expansion commences, and beneath this the broad surface is divided 
into two distinct, apparently articular, facettes. The upper and 
hinder division (a) is slightly hollowed and somewhat triangular in 
shape ; while the lower facette (4) is more elongated, and is separated 
from the first in its anterior portion by being more deeply impressed 
in the bone. 
Among the crushed cranial bones, immediately behind the sclerotic 
plates, in another specimen of JeAthyosaurus in the National Collec- 
tion the culumella is also distinctly visible; but this does not supply 
any additional facts of importance. 
On comparing the bone under consideration with its homologue 
among recent Reptiles, none is found to exhibit a more striking 
similarity than that of Hatteria (fig. 4, p. 407). As Dr. Ginther has 
pointed out’, the columella in this genus is particularly remarkable 
for the great expansion of its extremities ; and it is also peculiar from 
the fact that the lower end articulates not only with the pterygoid, 
but also with an inward extension of the quadrate. Moreover, so 
far as can be ascertained from a complete skull, the columella 
appears to show some signs of contracting this articulation by an 
overlapping of the two bones in a vertical plane; and the upper end 
is connected with cartilage, and not directly in contact with the 
parietal above. 
Unfortunately at present it is only possible to compare the form 
of the element in each of these types. In none of the fossil Ichthyo- 
saurs 1 have examined are the precise relations of the bone very 
distinct. As already stated, however, the first fossil is remarkably 
suggestive of a direct articulation of the upper end of thecolumella with 
a downward process of the parietal ; and the originals of figs. 2 and 3 
exhibit so close a resemblance to the corresponding parts in Hatleria, 
that there is also strong evidence of the lower articulation being 
double. But it ought to be remarked that in Ichthyosaurus no 
inwardly directed extension of the quadrate has hitherto been 
observed *, and the discovery of more satisfactory specimens must yet 
be awaited before it is possible to arrive at any definite conclusion. 
1 A. Giinther, “Contribution to the Anatomy of Hatteria (Rhynchocephalus, 
Owen),” Phil. Trans. 1867, p. 599, pl. xxvi. figs. 3, 4. 
* Hi. G. Seeley, “ Similitudes of the Bones in the Enaliosauria,” Journ. Linn. 
Soe. (Zoology) vol. xii. (1876), p. 309. 
